The present invention relates to a thermopile device, especially to a thermal isolation structure for a micro thermopile and method for making the same.
The conventional thermal isolation methods for micro thermopile devices are generally classified into the frontside etching process and the backside etching process. FIG. 1 shows the perspective view of a micro thermopile device fabricated by a conventional frontside etching process, and FIG. 2 shows the top view thereof. The micro thermopile device shown in FIGS. 1 and 2 is fabricated through following process: preparing a silicon substrate 12, forming a one-layer or multi-layer membrane 14 on the surface of the silicon substrate 12; forming black body 13 and thermopile 15 on the membrane 14, defining a plurality of etching windows 16, performing anisotropic etching to the silicon substrate 12 through the etching windows 16 and forming a pit between the silicon substrate 12 and the membrane 14 such that the membrane 14 becomes a floating membrane 18 and has thermal isolation with the silicon substrate 12.
However, in the above mentioned process, the trench below each of the etching windows 16 should overlap each other to form the pit, therefore, the area of the floating membrane 18 restricted by the etching windows 16 is relatively smaller. Moreover, the etching of the silicon substrate 12 below the center of the floating membrane 18 takes considerable time such that the floating membrane 18 probably cracks.
It is an object of the present invention to provide a thermal isolation structure for micro thermopile and the method making the same, by which the area of the floating membrane is increased and the strain of the floating membrane is reduced.
To achieve above objects, the present invention provides a method for forming thermal isolation for a micro thermopile device. The micro thermopile device has a silicon substrate and a one-layer or multi-layer membrane on the silicon substrate. The inventive method comprises steps of forming a narrow etching window on the membrane and forming a plurality of micro connection structures each crossing the narrow etching window and connecting the edge portion of the membrane on both sides of the narrow etching window, and etching the silicon substrate through the narrow etching window to form a pit between the silicon substrate and the membrane, whereby the membrane becomes a floating membrane and has thermal isolation with the silicon substrate.